The long-term objective of this project is to obtain a better understanding of the control mechanisms involved in regulating the processes of self-renewal, proliferation, and differentiation in hematopoietic stem/progenitor cells. This understanding is necessary in order to rationally manipulate these cells for optimal use in the correction of genetic defects, for autologous bone marrow transplantation in general, and to decrease the side effects of antineoplastic chemotherapy. Our laboratories have committed to a long term collaborative effort to study the molecular and cellular biology of human hematopoietic stem cells. Our premise is that the isolation of new genes expressed in these cells, together with the delineation of the function of these genes, will provide the information and tools to expand and differentiate human hematopoietic stem cells for multiple clinical uses. This approach has already resulted in the isolation of a growth factor receptor we call STK-1, which is the human homolog of FLK-2/FLT3. STK-1 is expressed selectively in the CD34+ stem/progenitor fraction of human bone marrow. We propose to use an chimeric STK-1 receptor to expand and potentially modulate hematopoietic stem cells engineered to express it. We also propose using anti-STK-1 monoclonal antibody to purify and study the normal marrow cell fraction physiologically expressing this receptor. We have recently isolated another novel tyrosine kinase from CD34+ cells. STK-2 is the newest member of the Jak family of tyrosine kinases. The other three Jak family members play critical roles in the signaling pathways involving the interferon, erythropoietin, growth hormone, lL- 3,GM-CSF, LIF, CNTF, IL-6 and OSM receptors. Because of its high level expression in the CD34+/lin- fraction of human bone marrow, it is likely that STK-2 plays a similar role in these cells. We therefore propose to study the role of STK-2 in these human marrow stem/progenitor cells. The isolation and study of other genes expressed by HSC will become an important part of this project in later years. We have already isolated a novel zinc finger protein (SZF-1) from CD34+ cells, and we will attempt to clone additional genes that we hope will prove important in hematopoietic stem cell function. In summary, we have isolated and are currently studying three novel genes, expressed by the human CD34+ marrow cells. These molecules span the information network of the cell from the cell surface to the cytoplasm to the nucleus. Studying these and similar novel genes to be isolated will increase fundamental understanding of the processes of self-renewal, proliferation, and differentiation in hematopoietic stem cells. This understanding should translate to improved therapy of a broad range of human diseases.